Electrophotographic photoreceptors employing inorganic photoconductive substances such as selenium, cadmium sulfide and zinc oxide have been replaced rapidly by photoreceptors (OPC) employing organic photoconductive substances. The reason for this is that organic photoconductive substances can offer various materials through combination of synthetic substances and synthesis conditions and thereby can offer a wide range of selection so that desired photoreceptors meeting the purpose can be prepared easily.
In OPCs, the function-separation type wherein a material bearing a function to generate carriers and a material bearing a function to convey carriers are different each other, the range of selection of materials has further been broadened, resulting in expectation of improvement in electrophotographic properties such as charging ability, sensitivity and durability.
As methods for forming a carrier generated layer (CGL) in a photoreceptor, gaseous phase deposition methods such as a vacuum evaporation method, a spattering method and CVD as well as coating methods such as dipping, spraying, blade and roll methods are employed.
Among them, when forming through a coating method, coatings for a carrier generated layer (CGL solution) wherein an organic photoconductive pigment (carrier generated material: CGM) is dispersed in an organic solvent are employed in many cases.
Properties required for the above-mentioned CGL solution,
--dispersion property of CGM is good PA1 --can be coated uniformly without defects PA1 --physical properties of the solution such as fluidity and particle size distribution in manufacturing of a photoreceptor is manufactured and electrophotographic properties of photoreceptor are stable PA1 --durable against repeated use PA1 --no change in properties occurs after being stocked for a long time
On the other hand, as CGMs used for the above-mentioned function-separation type photoreceptors, various organic dyes or organic pigments have been proposed. For example, multi-ring quinone pigments, pyrylium dyes, perylene pigments, indigoid pigments, phthalocyanine pigments and azo pigments have been put into practical use.
In the above-mentioned CGMs, enhancement of sensitivity can be contrived by providing specific coagulation structure or crystal structure in the course of setting their manufacturing conditions. However, it is difficult to set conditions of dispersion for keeping the above-mentioned structures after CGMs are processed to dispersion solutions. Accordingly, those satisfying all properties such as charging ability, sensitivity and repetitive property have not been obtained. Especially, in terms of sensitivity, further enhancement of sensitivity and stability are demanded.
As a technology coping with the above-mentioned demand, one wherein a specific titanyl type phthalocyanine is dispersed into a specific organic solvent is disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter, referred to as Japanese Patent O.P.I. Publication) No. 33859/1991.
However, improvement caused by the consumption manner of the solution in mass production of a photoreceptor employing a dispersion solution containing an azo pigment as a CGM and deterioration in a CGL solution in terms of change in crystal shape, absorbancy spectra and photo-sensitivity is not yet enough. In addition, when the life of solution is short as mentioned above, replacement of dispersion solution becomes frequent, causing high cost. Therefore, improvement in such issues is also demanded.